This invention relates to a method and an apparatus for raising a sample of liquid such as water from a low level to a higher level, for example for obtaining a sample of groundwater from a borehole.
A variety of methods are known for obtaining samples of liquids from boreholes. For example in the oil industry coiled tubing units are commonly used to transmit sample fluids from a particular zone in the borehole to the surface. Alternative techniques use a tool suspended on a wireline. Both these approaches are mentioned in U.S. Pat. No. 5,289,875 (Stokley et al). Such tools may incorporate packers to restrict the section of the borehole from which the fluid is obtained. However, such tools are complex, and it would be desirable to provide a simpler way of obtaining samples, which would be applicable over a wide range of different depths. The samples may be withdrawn for analysis, or alternatively the process may be repeated many times to empty a section of the borehole, that is to say using the sampler as a pump.